In the medical field, multi-way cocks, typically three-way cocks are widely used for various purposes including transfusion of blood and infusion of fluid medicaments such as glucose fluid and physiological saline to patients. Infusion systems often use a plurality of fluid medicaments which should be kept separate until infusion. A three-way cock involved in the system is manipulated such that selected fluid medicaments may be either separately or simultaneously infused into the patient. Also in blood transfusion systems, three-way cocks are often useful in introducing a desired medicament into transfusing blood or in alternating blood transfusion and fluid infusion.
In general, the three-way cocks are composed of a housing including a cylinder having three T-shaped branch tubes extending from the periphery thereof. A plug is combined with the housing, which includes a barrel adapted to be rotatably fitted in the cylinder and having three T-shaped channels corresponding to the branch tubes. A manual lever is attached to the top of the plug barrel for rotating the plug in the cylinder. By manipulating the lever, the plug can be rotated over an angle of 180 degrees with respect to the housing. When the lever is at one of angular positions, two of the three branch tubes are selectively brought in fluid communication through corresponding channels in the plug barrel while the remaining branch tube is shut off from communication. The cock assembly in which the plug is snugly fitted in the housing is required to be highly tight against fluid under pressure and durable in that such high fluid tightness is maintained over a number of plug changeovers (for example, 200 cycles of back-and-forth rotation).
Conventional three-way cocks generally have housings formed of rigid resin materials such as polycarbonate. For the plug, more particularly its barrel, high density polyethylene is often used because of biological compatibility, workability, and low cost. With this combination, however, the housing material is rather less compatible with the plug material, and the plug barrel is susceptible to failure as by scraping and abrasion when the plug is fitted in the housing or when the plug is rotated during service. Such failure often occurs at or near the edge of the openings that the channels define at the outer surface of the barrel.
In recent years, the development of three-way cocks accommodating an increased flow rate is desired in order to accelerate blood and fluid infusion processes. To this end, the channels in the plug barrel should be enlarged to a larger diameter than the currently used one. If the channel diameter, that is, the diameter of the opening that the channel defines at the barrel outer surface is increased, the circumference of the opening is accordingly increased, resulting in increased chances of failure. Since the three-way cock is designed such that a pressure resistant fluid tight seal is established by close engagement of the housing cylinder's inner surface with the plug barrel's outer surface in assembled condition, a failure will leave a gap in the engagement, resulting in a loss of fluid tight seal. In addition, if chips or fragments are produced by chipping or scraping, such fragments can be conveyed into the blood or fluid to be infused, imposing potential damage to the patient. The use of such three-way cocks is not recommended in the medical field.
Therefore, an object of the present invention is to provide a novel and improved multi-way cock in which the plug barrel can be formed with larger diameter channels than in the prior art and is fully resistant to damage as by scraping and abrasion upon insertion of the plug into the housing or during the heavy duty service.